LEA proteins are involved in cyst desiccation resistance and other abiotic stresses in Azotobacter vinelandii

HcLEA113, a late embryogenesis abundant protein gene, positively regulates drought-stress responses in kenaf

Late embryogenesis abundant (LEA) proteins have been widely recognized for their role in various abiotic stress responses in higher plants. Nevertheless, the specific mechanism responsible for the function of LEA proteins in plants has not yet been explored. This research involved the isolation and characterization of HcLEA113 from kenaf, revealing a significant increase in its expression in response to drought stress. When HcLEA113 was introduced into yeast, it resulted in an improved survival rate under drought conditions. Furthermore, the overexpression of HcLEA113 in tobacco plants led to enhanced tolerance to drought stress. Specifically, HcLEA113-OE plants exhibited higher germination rates, longer root lengths, greater chlorophyll content, and higher relative water content under drought stress compared to wild-type (WT) plants, while their relative conductivity was significantly lower than that of WT plants. Further physiological measurements revealed that the proline content, soluble sugars, and antioxidant activities of WT and HcLEA113-OE tobacco leaves increased significantly under drought stress, with greater changes in HcLEA113-OE plants than WT. The increase in hydrogen peroxide (H2O2), superoxide anions (O2 -), and malondialdehyde (MDA) content was significantly lower in HcLEA113-OE lines than in WT plants. Additionally, HcLEA113-OE plants can activate reactive oxygen species (ROS)- and osmotic-related genes in response to drought stress. On the other hand, silencing the HcLEA113 gene through virus-induced gene silencing (VIGS) in kenaf plants led to notable growth suppression when exposed to drought conditions, manifesting as decreased plant height and dry weight. Meanwhile, antioxidant enzymes' activity significantly decreased and the ROS content increased. This study offers valuable insights for future research on the genetic engineering of drought resistance in plants.

The Azotobacter vinelandii AlgU regulon during vegetative growth and encysting conditions: A proteomic approach

In the Pseduomonadacea family, the extracytoplasmic function sigma factor AlgU is crucial to withstand adverse conditions. Azotobacter vinelandii, a closed relative of Pseudomonas aeruginosa, has been a model for cellular differentiation in Gram-negative bacteria since it forms desiccation-resistant cysts. Previous work demonstrated the essential role of AlgU to withstand oxidative stress and on A. vinelandii differentiation, particularly for the positive control of alginate production. In this study, the AlgU regulon was dissected by a proteomic approach under vegetative growing conditions and upon encystment induction. Our results revealed several molecular targets that explained the requirement of this sigma factor during oxidative stress and extended its role in alginate production. Furthermore, we demonstrate that AlgU was necessary to produce alkyl resorcinols, a type of aromatic lipids that conform the cell membrane of the differentiated cell. AlgU was also found to positively regulate stress resistance proteins such as OsmC, LEA-1, or proteins involved in trehalose synthesis. A position-specific scoring-matrix (PSSM) was generated based on the consensus sequence recognized by AlgU in P. aeruginosa, which allowed the identification of direct AlgU targets in the A. vinelandii genome. This work further expands our knowledge about the function of the ECF sigma factor AlgU in A. vinelandii and contributes to explains its key regulatory role under adverse conditions.

Ammonia-oxidizing archaea and bacteria differentially contribute to ammonia oxidation in soil under precipitation gradients and land legacy

Background

Global change has accelerated the nitrogen cycle. Soil nitrogen stock degradation by microbes leads to the release of various gases, including nitrous oxide (N2O), a potent greenhouse gas. Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) participate in the soil nitrogen cycle, producing N2O. There are outstanding questions regarding the impact of environmental processes such as precipitation and land use legacy on AOA and AOB structurally, compositionally, and functionally. To answer these questions, we analyzed field soil cores and soil monoliths under varying precipitation profiles and land legacies.

Results

We resolved 28 AOA and AOB metagenome assembled genomes (MAGs) and found that they were significantly higher in drier environments and differentially abundant in different land use legacies. We further dissected AOA and AOB functional potentials to understand their contribution to nitrogen transformation capabilities. We identified the involvement of stress response genes, differential metabolic functional potentials, and subtle population dynamics under different environmental parameters for AOA and AOB. We observed that AOA MAGs lacked a canonical membrane-bound electron transport chain and F-type ATPase but possessed A/A-type ATPase, while AOB MAGs had a complete complex III module and F-type ATPase, suggesting differential survival strategies of AOA and AOB.

Conclusions

The outcomes from this study will enable us to comprehend how drought-like environments and land use legacies could impact AOA- and AOB-driven nitrogen transformations in soil.

Genome-wide identification and expression analysis of late embryogenesis abundant (LEA) genes reveal their potential roles in somatic embryogenesis in hybrid sweetgum (Liquidambar styraciflua × Liquidambar formosana)

Late embryogenesis abundant (LEA) proteins are widely distributed in higher plants that play significant roles in embryonic development and abiotic stress response. Hybrid sweetgum is an important forest tree resource around the world, and somatic embryogenesis is an efficient way of reproduction and utilization. However, a systematic analysis of the LEA family genes in hybrid sweetgum is lacking, this is not conducive to the efficiency of its somatic embryogenesis. From the whole genome of the hybrid sweetgum, utilizing hidden Markov models, an identification of a total of 79 LEA genes was successfully conducted. They were classified into eight different groups based on their conserved domains and phylogenetic relationships, with the LsfLEA2 group of genes being the most abundant. The gene structure and sequence characteristics and chromosomal localization, as well as the physicochemical properties of LEA proteins were meticulously carried out. Analysis of the cis-acting elements shows that most of the LsfLEA genes are associated with light-responsive-elements. In addition, some genes are associated with biosynthetic pathways, such as abscisic acid response, growth hormone response, methyl jasmonate response, somatic embryogenesis, meristematic tissue expression. Furthermore, we systematically analyzed the expression patterns of hybrid sweetgum LEA genes in different stages of somatic embryogenesis and different tissues, in LEA family genes we also found significant specificity in gene expression during somatic embryogenesis. This study provides new insights into the formation of members of the LsfLEA family genes in hybrid sweetgum, while improving the understanding of the potential role of these genes in the process of hybrid sweetgum somatic embryogenesis and abiotic stress response. These results have a certain guiding significance for the future functional study of LsfLEA family genes, and provide a theoretical basis for exploring the regulatory mechanism of LsfLEA genes in the somatic embryo development stage of hybrid sweetgum.

Artificial Proteins Designed from G3LEA Contribute to Enhancement of Oxidation Tolerance in E. coli in a Chaperone-like Manner

G3LEA is a family of proteins that exhibit chaperone-like activity when under distinct stress. In previous research, DosH was identified as a G3LEA protein from model extremophile-Deinococcus radiodurans R1 with a crucial core HD domain consisting of eight 11-mer motifs. However, the roles of motifs participating in the process of resistance to stress and their underlying mechanisms remain unclear. Here, eight different proteins with tandem repeats of the same motif were synthesized, named Motif1-8, respectively, whose function and structure were discussed. In this way, the role of each motif in the HD domain can be comprehensively analyzed, which can help in finding possibly crucial amino acid sites. Circular dichroism results showed that all proteins were intrinsically ordered in phosphate buffer, and changed into more α-helical ordered structures with the addition of trifluoroethanol and glycerol. Transformants expressing artificial proteins had significantly higher stress resistance to oxidation, desiccation, salinity and freezing compared with the control group; E. coli with Motif1 and Motif8 had more outstanding performance in particular. Moreover, enzymes and membrane protein protection viability suggested that Motif1 and Motif8 had more positive influences on various molecules, demonstrating a protective role in a chaperone-like manner. Based on these results, the artificial proteins synthesized according to the rule of 11-mer motifs have a similar function to wildtype protein. Regarding the sequence in all motifs, there are more amino acids to produce H bonds and α-helices, and more amino acids to promote interaction between proteins in Motif1 and Motif8; in addition, considering linkers, there are possibly more amino acids forming α-helix and binding substrates in these two proteins, which potentially provides some ideas for us to design potential ideal stress-response elements for synthetic biology. Therefore, the amino acid composition of the 11-mer motif and linker is likely responsible for its biological function.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

LEAfing through literature: late embryogenesis abundant proteins coming of age-achievements and perspectives

To deal with increasingly severe periods of dehydration related to global climate change, it becomes increasingly important to understand the complex strategies many organisms have developed to cope with dehydration and desiccation. While it is undisputed that late embryogenesis abundant (LEA) proteins play a key role in the tolerance of plants and many anhydrobiotic organisms to water limitation, the molecular mechanisms are not well understood. In this review, we summarize current knowledge of the physiological roles of LEA proteins and discuss their potential molecular functions. As these are ultimately linked to conformational changes in the presence of binding partners, post-translational modifications, or water deprivation, we provide a detailed summary of current knowledge on the structure-function relationship of LEA proteins, including their disordered state in solution, coil to helix transitions, self-assembly, and their recently discovered ability to undergo liquid-liquid phase separation. We point out the promising potential of LEA proteins in biotechnological and agronomic applications, and summarize recent advances. We identify the most relevant open questions and discuss major challenges in establishing a solid understanding of how these intriguing molecules accomplish their tasks as cellular sentinels at the limits of surviving water scarcity.

Evaluation of a bacterial group 1 LEA protein as an enzyme protectant from stress-induced inactivation

Late embryogenesis abundant (LEA) proteins are hydrophilic proteins that lack a well-ordered tertiary structure and accumulate to high levels in response to water deficit, in organisms such as plants, fungi, and bacteria. The mechanisms proposed to protect cellular structures and enzymes are water replacement, ion sequestering, and membrane stabilization. The activity of some proteins has a limited shelf-life due to instability that can be caused by their structure or the presence of a stress condition that limits their activity; several LEA proteins have been shown to behave as cryoprotectants in vitro. Here, we report a group1 LEA from Azotobacter vinelandii AvLEA1, capable of conferring protection to lactate dehydrogenase, catechol dioxygenase, and Baylase peroxidase against freeze-thaw treatments, desiccation, and oxidative damage, making AvLEA a promising biological stabilizer reagent. This is the first evidence of protection provided by this LEA on enzymes with biotechnological potential, such as dioxygenase and peroxidase under in vitro stress conditions. Our results suggest that AvLEA could act as a molecular chaperone, or a "molecular shield," preventing either dissociation or antiaggregation, or as a radical scavenger, thus preventing damage to these target enzymes during induced stress. KEY POINTS: • This work expands the basic knowledge of the less-known bacterial LEA proteins and their in vitro protection potential. • AvLEA is a bacterial protein that confers in vitro protection to three enzymes with different characteristics and oligomeric arrangement. • The use of AvLEA as a stabilizer agent could be further explored using dioxygenase and peroxidase in bioremediation treatments. AvLEA1 protects against freeze-thaw treatments, desiccation, and oxidative damage on three different enzymes with biotechnological potential.

Characterization of a Novel TtLEA2 Gene From Tritipyrum and Its Transformation in Wheat to Enhance Salt Tolerance

Late embryogenesis-abundant (LEA) proteins are critical in helping plants cope with salt stress. "Y1805" is a salt-tolerant Tritipyrum. We identified a "Y1805"-specific LEA gene that was expressed highly and sensitively under salt stress using transcriptome analysis. The novel group 2 LEA gene (TtLEA2-1) was cloned from "Y1805." TtLEA2-1 contained a 453 bp open reading frame encoding an 151-amino-acid protein that showed maximum sequence identity (77.00%) with Thinopyrum elongatum by phylogenetic analysis. It was mainly found to be expressed highly in the roots by qRT-PCR analysis and was located in the whole cell. Forty-eight candidate proteins believed to interact with TtLEA2-1 were confirmed by yeast two-hybrid analysis. These interacting proteins were mainly enriched in "environmental information processing," "glycan biosynthesis and metabolism," and "carbohydrate metabolism." Protein-protein interaction analysis indicated that the translation-related 40S ribosomal protein SA was the central node. An efficient wheat transformation system has been established. A coleoptile length of 2 cm, an Agrobacteria cell density of 0.55-0.60 OD₆₀₀, and 15 KPa vacuum pressure were ideal for common wheat transformation, with an efficiency of up to 43.15%. Overexpression of TaLEA2-1 in wheat "1718" led to greater height, stronger roots, and higher catalase activity than in wild type seedlings. TaLEA2-1 conferred enhanced salt tolerance in transgenic wheat and may be a valuable gene for genetic modification in crops.

Pöllänen M, Johansson A, Permi P, Ihalin R. Decreased temperature increases the expression of a disordered bacterial late embryogenesis abundant (LEA) protein that enhances natural transformation

Late embryogenesis abundant (LEA) proteins are important players in the management of responses to stressful conditions, such as drought, high salinity, and changes in temperature. Many LEA proteins do not have defined three-dimensional structures, so they are intrinsically disordered proteins (IDPs) and are often highly hydrophilic. Although LEA-like sequences have been identified in bacterial genomes, the functions of bacterial LEA proteins have been studied only recently. Sequence analysis of outer membrane interleukin receptor I (BilRI) from the oral pathogen Aggregatibacter actinomycetemcomitans indicated that it shared sequence similarity with group 3/3b/4 LEA proteins. Comprehensive nuclearcgq magnetic resonance (NMR) studies confirmed its IDP nature, and expression studies in A. actinomycetemcomitans harboring a red fluorescence reporter protein-encoding gene revealed that bilRI promoter expression was increased at decreased temperatures. The amino acid backbone of BilRI did not stimulate either the production of reactive oxygen species from human leukocytes or the production of interleukin-6 from human macrophages. Moreover, BilRI-specific IgG antibodies could not be detected in the sera of A. actinomycetemcomitans culture-positive periodontitis patients. Since the bilRI gene is located near genes involved in natural competence (i.e., genes associated with the uptake of extracellular (eDNA) and its incorporation into the genome), we also investigated the role of BilRI in these events. Compared to wild-type cells, the ΔbilRI mutants showed a lower transformation efficiency, which indicates either a direct or indirect role in natural competence. In conclusion, A. actinomycetemcomitans might express BilRI, especially outside the host, to survive under stressful conditions and improve its transmission potential.

Xerotolerance: A New Property in Exiguobacterium Genus

The highly xerotolerant bacterium classified as Exiguobacterium sp. Helios isolated from a solar panel in Spain showed a close relationship to Exiguobacterium sibiricum 255-15 isolated from Siberian permafrost. Xerotolerance has not been previously described as a characteristic of the extremely diverse Exiguobacterium genus, but both strains Helios and 255-15 showed higher xerotolerance than that described in the reference xerotolerant model strain Deinococcus radiodurans. Significant changes observed in the cell morphology after their desiccation suggests that the structure of cellular surface plays an important role in xerotolerance. Apart from its remarkable resistance to desiccation, Exiguobacterium sp. Helios strain shows several polyextremophilic characteristics that make it a promising chassis for biotechnological applications. Exiguobacterium sp. Helios cells produce nanoparticles of selenium in the presence of selenite linked to its resistance mechanism. Using the Lactobacillus plasmid pRCR12 that harbors a cherry marker, we have developed a transformation protocol for Exiguobacterium sp. Helios strain, being the first time that a bacterium of Exiguobacterium genus has been genetically modified. The comparison of Exiguobacterium sp. Helios and E. sibiricum 255-15 genomes revealed several interesting similarities and differences. Both strains contain a complete set of competence-related DNA transformation genes, suggesting that they might have natural competence, and an incomplete set of genes involved in sporulation; moreover, these strains not produce spores, suggesting that these genes might be involved in xerotolerance.

Effects of AavLEA1 Protein on Mouse Ovarian Tissue Cryopreservation by Vitrification

Conventional ovarian tissue cryopreservation often destroys the structural, functional, and DNA integrity of the ovarian tissue. How to effectively retain the ultrastructure and subsequent function of ovarian tissue during cryopreservation has long been an issue of concern. Late embryogenesis abundant (LEA) proteins are a class of highly hydrophilic proteins and have been reported to protect various cells from water stress. However, whether LEA proteins exert protective effects on ovarian tissue cryopreservation remains unknown. To investigate the benefit of LEA proteins in ovarian tissue cryopreservation, we purified the recombinant AavLEA1 protein, a member of Group 3 LEA proteins, then cryopreserved the mouse ovaries with this protein by vitrification, and obtained the ovarian follicle structure, cellular proliferation, apoptosis, and GAPDH gene expression of postcryopreservation ovaries. We found that recombinant AavLEA1 protein protected the ovarian follicles from cryoinjury, improved the proliferative ability of follicles, decreased the apoptosis, and promoted the GAPDH gene expression. These results indicated that the LEA protein enhanced the antiapoptosis ability of ovarian cells and retained DNA/RNA integrity against cryoinjury during ovarian tissue vitrification. LEA proteins exert beneficial effects on ovarian tissue cryopreservation, and maybe provide a novel cryoprotective agent for ovarian tissue cryopreservation.

OsLEA1a overexpression enhances tolerance to diverse abiotic stresses by inhibiting cell membrane damage and enhancing ROS scavenging capacity in transgenic rice

Late embryogenesis abundant (LEA) proteins are involved in diverse abiotic stresses tolerance in many different organisms. Our previous studies have shown that the heterologous expression of OsLEA1a interfered with the resistance of Escherichia coli to abiotic stresses. However, in the present study, based on growth status and physiological indices of rice plant, the overexpression of OsLEA1a in rice conferred increased resistance to abiotic stresses compared with the wild-type (WT) plants. Before applying abiotic stresses, there were no significant differences in physiological indices of rice seedlings. After NaCl, sorbitol, CuSO4 and H2O2 stresses, the transgenic lines had lower relative electrical conductivity, malondialdehyde and lipid peroxidation, greater the contents of proline, soluble sugar and glutathione, and higher the activities of superoxide dismutase, catalase and peroxidase than the WT plants. The results indicate that the OsLEA1a gene is involved in the protective response of plants to various abiotic stresses by inhibiting cell membrane damage and enhancing reactive oxygen species scavenging capacity. It was speculated that post-translational modification causes OsLEA1a functional differences in E. coli and rice. The present study shows that OsLEA1a could be a useful candidate gene for engineering abiotic stress tolerance in cultivated plants.

Late embryogenesis abundant (LEA) gene family in Salvia miltiorrhiza: identification, expression analysis, and response to drought stress

Late embryogenesis abundant (LEA) proteins play important roles in plant defense response to drought stress. However, genome-wide identification of the LEA gene family was not revealed in Salvia miltiorrhiza. In this study, 61 SmLEA genes were identified from S. miltiorrhiza and divided into 7 subfamilies according to their conserved domains and phylogenetic relationships. SmLEA genes contained the LEA conserved motifs and few introns. SmLEA genes of the same subfamilies had similar gene structures and predicted subcellular locations. Our results indicated that the promoters of SmLEA genes contained various cis-acting elements associated with abiotic stress response. In addition, RNA-seq and real-time PCR results suggested that SmLEA genes are specifically expressed in different tissue, and most SmLEA genes can be induced by drought stress. These results provide a valuable foundation for future functional investigations of SmLEA genes and drought stress-resistant breeding of S. miltiorrhiza.

Target enzymes are stabilized by AfrLEA6 and a gain of α-helix coincides with protection by a group 3 LEA protein during incremental drying

Anhydrobiotic organisms accumulate late embryogenesis abundant (LEA) proteins, a family of intrinsically disordered proteins (IDPs) reported to improve cellular tolerance to water stress. Here we show that AfrLEA6, a Group 6 LEA protein only recently discovered in animals, protects lactate dehydrogenase (LDH), citrate synthase (CS) and phosphofructokinase (PFK) against damage during desiccation. In some cases, protection is enhanced by trehalose, a naturally-occurring protective solute. An open question is whether gain of secondary structure by LEA proteins during drying is a prerequisite for this stabilizing function. We used incremental drying (equilibration to a series of relative humidities, RH) to test the ability of AfrLEA2, a Group 3 LEA protein, to protect desiccation-sensitive PFK. AfrLEA2 was chosen due to its exceptional ability to protect PFK. In parallel, circular dichroism (CD) spectra were obtained for AfrLEA2 across the identical range of relative water contents. Protection of PFK by AfrLEA2, above that observed with trehalose and BSA, coincides with simultaneous gain of α-helix in AfrLEA2. At 100% RH, the CD spectrum for AfrLEA2 is typical of random coil, while at decreasing RH, the spectrum shows higher ellipticity at 191 nm and minima at 208 and 220 nm, diagnostic of α-helix. This study provides experimental evidence linking the gain of α-helix with stabilization of a target protein across a graded series of hydration states. Mechanistically, it is intriguing that certain other functions of these IDPs, like preventing aggregation of target proteins, can occur in fully hydrated cells and apparently do not require gain of α-helix.

Nitrogen Fixing Azotobacter Species as Potential Soil Biological Enhancers for Crop Nutrition and Yield Stability

Biological nitrogen fixation (BNF) refers to a microbial mediated process based upon an enzymatic "Nitrogenase" conversion of atmospheric nitrogen (N₂) into ammonium readily absorbable by roots. N₂-fixing microorganisms collectively termed as "diazotrophs" are able to fix biologically N₂ in association with plant roots. Specifically, the symbiotic rhizobacteria induce structural and physiological modifications of bacterial cells and plant roots into specialized structures called nodules. Other N₂-fixing bacteria are free-living fixers that are highly diverse and globally widespread in cropland. They represent key natural source of nitrogen (N) in natural and agricultural ecosystems lacking symbiotic N fixation (SNF). In this review, the importance of Azotobacter species was highlighted as both important free-living N₂-fixing bacteria and potential bacterial biofertilizer with proven efficacy for plant nutrition and biological soil fertility. In addition, we described Azotobacter beneficial plant promoting traits (e.g., nutrient use efficiency, protection against phytopathogens, phytohormone biosynthesis, etc.). We shed light also on the agronomic features of Azotobacter that are likely an effective component of integrated plant nutrition strategy, which contributes positively to sustainable agricultural production. We pointed out Azotobacter based-biofertilizers, which possess unique characteristics such as cyst formation conferring resistance to environmental stresses. Such beneficial traits can be explored profoundly for the utmost aim to research and develop specific formulations based on inoculant Azotobacter cysts. Furthermore, Azotobacter species still need to be wisely exploited in order to address specific agricultural challenges (e.g., nutrient deficiencies, biotic and abiotic constraints) taking into consideration several variables including their biological functions, synergies and multi-trophic interactions, and biogeography and abundance distribution.

Participation of two general stress response proteins from Xanthomonas citri subsp. citri in environmental stress adaptation and virulence

Xanthomonas citri subsp. citri (Xcc) is the bacteria responsible for citrus canker. During its life cycle Xcc is found on leaves as epiphyte, where desiccation conditions may occur. In this work, two Xcc genes, XAC0100 and XAC4007, predicted in silico to be involved in general stress response, were studied under salt, osmotic, desiccation, oxidative and freezing stress, and during plant-pathogen interaction. Expression of XAC0100 and XAC4007 genes was induced under these stress conditions. Disruption of both genes in Xcc caused decreased bacterial culturability under desiccation, freezing, osmotic and oxidative stress. Importantly, the lack of these genes impaired Xcc epiphytic fitness. Both Xac0100 and Xac4007 recombinant proteins showed protective effects on Xanthomonas cells subjected to drought stress. Also, Escherichia coli overexpressing Xac4007 showed a better performance under standard culture, saline and osmotic stress and were more tolerant to freezing and oxidative stress than wild type E. coli. Moreover, both Xac0100 and Xac4007 recombinant proteins were able to prevent the freeze-thaw-induced inactivation of L-Lactate dehydrogenase. In conclusion, Xac0100 and Xac4007 have a relevant role as bacteria and protein protectors; and these proteins are crucial to bacterial pathogens that must face environmental stressful conditions that compromise the accomplishment of the complete virulence process.

Transcriptomic Analysis of the Grapevine LEA Gene Family in Response to Osmotic and Cold Stress Reveals a Key Role for VamDHN3

Late embryogenesis abundant (LEA) proteins comprise a large family that plays important roles in the regulation of abiotic stress, however, no in-depth analysis of LEA genes has been performed in grapevine to date. In this study, we analyzed a total of 52 putative LEA genes in grapevine at the genomic and transcriptomic level, compiled expression profiles of four selected (V. amurensis) VamLEA genes under cold and osmotic stresses, and studied the potential function of the V. amurensis DEHYDRIN3 (VamDHN3) gene in grapevine callus. The 52 LEA proteins were classified into seven phylogenetic groups. RNA-seq and quantitative real-time PCR results demonstrated that a total of 16 and 23 VamLEA genes were upregulated under cold and osmotic stresses, respectively. In addition, overexpression of VamDHN3 enhanced the stability of the cell membrane in grapevine callus, suggesting that VamDHN3 is involved in osmotic regulation. These results provide fundamental knowledge for the further analysis of the biological roles of grapevine LEA genes in adaption to abiotic stress.

A Short Peptide Designed from Late Embryogenesis Abundant Protein Enhances Acid Tolerance in Escherichia coli

Unsuitable pH is a major limiting factor for all organisms, and a low pH can lead to organism death. Late embryogenesis abundant (LEA) peptides confer tolerance to abiotic stresses including salinity, drought, high and low temperature, and ultraviolet radiation same as the LEA proteins from which they originate. In this study, LEA peptides derived from group 3 LEA proteins of Polypedilum vanderplanki were used to enhance low pH tolerance. Recombinant Escherichia coli BL21 (DE3) cells expressing the five designed LEA peptides were grown at pH 4, 3, and 2. The transformants showed higher growth capacity at low pH as compared to control cells. These results indicate that LEA peptide could prevent E. coli cell death under low pH conditions.

Genome-wide identification of and functional insights into the late embryogenesis abundant (LEA) gene family in bread wheat (Triticum aestivum)

Late embryogenesis abundant (LEA) proteins are involved in the responses and adaptation of plants to various abiotic stresses, including dehydration, salinity, high temperature, and cold. Here, we report the first comprehensive survey of the LEA gene family in “Chinese Spring” wheat (Triticum aestivum). A total of 179 TaLEA genes were identified in T. aestivum and classified into eight groups. All TaLEA genes harbored the LEA conserved motif and had few introns. TaLEA genes belonging to the same group exhibited similar gene structures and chromosomal locations. Our results revealed that most TaLEA genes contained abscisic acid (ABA)-responsive elements (ABREs) and various cis-acting elements associated with the stress response in the promoter region and were induced under ABA and abiotic stress treatments. In addition, 8 genes representing each group were introduced into E. coli and yeast to investigate the protective function of TaLEAs under heat and salt stress. TaLEAs enhanced the tolerance of E. coli and yeast to salt and heat, indicating that these proteins have protective functions in host cells under stress conditions. These results increase our understanding of LEA genes and provide robust candidate genes for future functional investigations aimed at improving the stress tolerance of wheat.

Structural properties and cellular expression of AfrLEA6, a group 6 late embryogenesis abundant protein from embryos of Artemia franciscana

Late embryogenesis abundant (LEA) proteins are intrinsically disordered proteins (IDPs) commonly found in anhydrobiotic organisms and are frequently correlated with desiccation tolerance. Herein we report new findings on AfrLEA6, a novel group 6 LEA protein from embryos of Artemia franciscana. Assessment of secondary structure in aqueous and dried states with circular dichroism (CD) reveals 89% random coil in the aqueous state, thus supporting classification of AfrLEA6 as an IDP. Removal of water from the protein by drying or exposure to trifluoroethanol (a chemical de-solvating agent) promotes a large gain in secondary structure of AfrLEA6, predominated by α-helix and exhibiting minimal β-sheet structure. We evaluated the impact of physiological concentrations (up to 400 mM) of the disaccharide trehalose on the folding of LEA proteins in solution. CD spectra for AfrLEA2, AfrLEA3m, and AfrLEA6 are unaffected by this organic solute noted for its ability to drive protein folding. AfrLEA6 exhibits its highest concentration in vivo during embryonic diapause, drops acutely at diapause termination, and then declines during development to undetectable values at the larval stage. Maximum cellular titer of AfrLEA6 was 10-fold lower than for AfrLEA2 or AfrLEA3, both group 3 LEA proteins. Acute termination of diapause with H2O2 (a far more effective terminator than desiccation in this Great Salt Lake, UT, population) fostered a rapid 38% decrease in AfrLEA6 content of embryos. While the ultimate mechanism of diapause termination is unknown, disruption of key macromolecules could initiate physiological signaling events necessary for resumption of development and metabolism.

Overexpression of OsLea14-A improves the tolerance of rice and increases Hg accumulation under diverse stresses

The group 5 LEA (late embryogenesis abundant) proteins are an atypical LEA protein group, which is associated with resistance to multiple stresses. In this study, OsLea14-A gene was isolated from Oryza sativa L., which encodes a 5C LEA protein with 151 amino acids. The qPCR analysis showed that OsLea14-A expressed in all tissues and organs at all times. The expression of OsLea14-A in the panicles of plumping stage were dramatically increased. The heterologous expression of OsLea14-A in Escherichia coli improved its growth performance under salinity, desiccation, high temperature, and freeze-thaw stresses. The purified OsLea14-A protein can protect LDH activity from freeze-thaw-, heat-, and desiccation-induced inactivation. The overexpression of OsLea14-A in rice improved tolerance to dehydration, high salinity, CuSO₄, and HgCl₂, but excluding K₂Cr₂O₇. The analysis of metal contents showed that the accumulation of OsLea14-A protein in transgenic rice could increase the accumulation of Hg, but could not increase the accumulation of Na, Cr, and Cu after HgCl₂, NaCl, K₂Cr₂O₇, and CuSO₄ treatment, respectively. These results suggested that OsLea14-A conferred multiple stress tolerance and Hg accumulation, which made it a possible gene in genetic improvement for plants to acclimatize itself to multiple stresses and remediate Hg-contaminated soil.

Nanoparticle-Induced Changes in Resistance and Resilience of Sensitive Microbial Indicators towards Heat Stress in Soil

Modern agricultural innovations with nanomaterials are now being applied in every sphere of agriculture. However, their interaction with soil microbial processes is not being explored in detail. This initiative was undertaken to understand the effect of metal-oxide nanoparticles with heat stress in soil. Metal-oxide nanoparticles, zinc oxide (ZnO), and iron oxide (Fe2O3) (each at 10 and 40 mg kg−1 w/w) were mixed into uncontaminated soil and subjected to heat stress of 48 °C for 24 hours to assess their effect on soil biological indicators. The resistance indices for the acid (ACP), alkaline phosphatase (AKP) activity, and fluorescein diacetate hydrolyzing (FDA) activity (0.58 to 0.73, 0.58 to 0.66, and 0.42 to 0.48, respectively) were higher in the presence of ZnO nanoparticles as compared to Fe2O3 nanomaterials, following an unpredictable pattern at either 10 or 40 mg kg−1 in soils, except dehydrogenase activity (DHA), for which the activity did not change with ZnO nanomaterial. An explicit role of ZnO nanomaterial in the revival pattern of the enzymes was observed (0.20 for DHA, 0.39 for ACP, and 0.43 for AKP), except FDA, which showed comparable values with Fe2O3 nanomaterials for the following 90 day (d) after stress. Microbial count exhibiting higher resistance values were associated with Fe2O3 nanoparticles as compared to ZnO nanomaterials, except Pseudomonas. The recovery indices for the microbial counts were higher with the application of Fe2O3 nanomaterials (0.34 for Actinobacteria, 0.38 for fungi, 0.33 for Pseudomonas and 0.28 for Azotobacter). Our study emphasizes the fact that sensitive microbial indicators in soil might be hampered by external stress initially but do have the competency to recover with time, thereby reinstating the resistance and resilience of soil systems.

Cotton Late Embryogenesis Abundant (LEA2) Genes Promote Root Growth and Confer Drought Stress Tolerance in Transgenic Arabidopsis thaliana

Late embryogenesis abundant (LEA) proteins play key roles in plant drought tolerance. In this study, 157, 85 and 89 candidate LEA2 proteins were identified in G. hirsutum, G. arboreum and G. raimondii respectively. LEA2 genes were classified into 6 groups, designated as group 1 to 6. Phylogenetic tree analysis revealed orthologous gene pairs within the cotton genome. The cotton specific LEA2 motifs identified were E, R and D in addition to Y, K and S motifs. The genes were distributed on all chromosomes. LEA2s were found to be highly enriched in non-polar, aliphatic amino acid residues, with leucine being the highest, 9.1% in proportion. The miRNA, ghr-miR827a/b/c/d and ghr-miR164 targeted many genes are known to be drought stress responsive. Various stress-responsive regulatory elements, ABA-responsive element (ABRE), Drought-responsive Element (DRE/CRT), MYBS and low-temperature-responsive element (LTRE) were detected. Most genes were highly expressed in leaves and roots, being the primary organs greatly affected by water deficit. The expression levels were much higher in G. tomentosum as opposed to G. hirsutum. The tolerant genotype had higher capacity to induce more of LEA2 genes. Over expression of the transformed gene Cot_AD24498 showed that the LEA2 genes are involved in promoting root growth and in turn confers drought stress tolerance. We therefore infer that Cot_AD24498, CotAD_20020, CotAD_21924 and CotAD_59405 could be the candidate genes with profound functions under drought stress in upland cotton among the LEA2 genes. The transformed Arabidopsis plants showed higher tolerance levels to drought stress compared to the wild types. There was significant increase in antioxidants, catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) accumulation, increased root length and significant reduction in oxidants, Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations in the leaves of transformed lines under drought stress condition. This study provides comprehensive analysis of LEA2 proteins in cotton thus forms primary foundation for breeders to utilize these genes in developing drought tolerant genotypes.